I find that penetrating oil almost always helps the situation, and certainly never hurts.
I like PB Blaster myself.
With the penetrating oil don't be afraid to also use a some time.
If it's moving but stubborn go forward and backward kind of gently to let the penetrating oil work in, then try harder to remove it.
For stubborn screws a hand impact driver is often helpful.
And if something does break off don't worry to much. Learn to use your welder to build up the bolt and grab onto it with some vicegrips, the concentrated heat of welding on the bolt works wonders!
Grigg
